I have used the Bose A20 and the Bose Proflight in-ear headsets. If you go for the Proflights, make sure it's version 2. That upgrade was well worth it.
They work best in a relatively quiet flight deck as in there's no ambient sound protection like you get with over the ear models (eg A30). They are very good for SA in that regards, (people behind you) and you can cancel the ANR individually or simply pull the ear piece out.
Sound quality and ANR is excellent, as you'd expect from a premium product. Mic sound was very good too. There is a fair bit of ANR adjustability too.
If your ears are used to Bose in ear headphones, you'll adjust in no time. Otherwise, I found I needed a day or two off the Proflights to let my ears adapt. After that, I had no trouble. They do feel they are going to slip off your head but they don't.
